The present invention relates to a tap hole mix containing essentially no binder, e.g., either water or tar (including pitch and asphalt) with or without the addition of a resin.
For blocking a tap hole of a blast furnace and the like, such mixes as a mix containing water and a mix using a binder comprising one or more of tar, pitch and asphalt with or without the addition of a resin have hitherto been used.
On the other hand, as a result of the development of a high burden operation under high pressure and high productivity in the blast furnace, a tap hole mix having following characteristics is now required.
A. a suitable plasticity necessary for plugging the tap hole with the use of a plugging gun, PA1 B. a rapidly hardening or setting property which exhibits sufficient strength after plugging the tap hole, PA1 C. excellent strength at higher temperatures and an excellent corrosion resistance against blast furnace molten pig iron and slag, PA1 D. provide for easy-opening of the tap hole, and PA1 E. avoid the emission of black smoke and abnormal dusts.
However, the conventional tap hole mixes hitherto used, such as, a mix containing water and a mix using an organic binder, do not satisfy said requisites simultaneously.
In applying a tap hole mix to a blast furnace, a mix is plugged into a tap hole through a plugging gun by attaching the gun close to the tap hole when one tapping is over, the plugging gun is held in this position until the mix exhibits a sufficient strength in the tap hole and is not pushed back against the furnace pressure or until the mix shows a sufficient strength to stop the flowing out of the melt in the furnace to the outside of the furnace. Then, the plugging gun is returned to the former position to finish the plugging of the tap hole. During a given period after plugging, molten pig iron and slag approach a definite level in the furnace, and then the tap hole is opened by an opener to tap the molten pig iron and slag out of the furnace. For example, in a blast furnace with a capacity of 2000 to 5000 tons per day, the tapping usually needs about 60 to 180 minutes, and the amount of pig iron per tapping is about 200 to 600 tons. The tapping is done 10 to 15 times a day.
The tap hole mixes hitherto used are chiefly of bonded tar type using tar (including pitch and asphalt) as a binder. Such mixes have no particular problems with respect to the plasticity in filling the mix in the tap hole, but have various problems in other respects. Since tar is thermoplastic, the mix is not rapidly hardened by the furnace heat after the mix is filled in the tap hole and does not bind completely to strengthen the mix sufficiently against the furnace pressure until the carbon-carbon bonds are formed by the carbonization of tar. Thus, the plugging gun must be held close to the tap hole continuously until the carbon-carbon bonds are sufficiently formed. For example, it requires more than 40 minutes until the bending strength of the mix becomes more than 10 kg/cm.sup.2 at 600.degree. C. During this time, the plugging gun is held close to the tap hole and the tapping operation from the tap hole is impossible, so that, in a blast furnace having only one tap hole and even in a furnace having several tap holes, the operation efficiency is lowered and accordingly the productivity of the furnace is also remarkably lowered.
Since tar is thermoplastic, the polymerisation of the binder proceeds with difficulty because of the furnace heat and the binder is carbonized in this condition as the carbon bonding does not occur. The formation of three dimensional carbon-carbon bonds does hardly take place and the bonding strength is very low. For example, the hot bending strength of the mix is only about 15 kg/cm.sup.2 at 1400.degree. C.
Further, the volatile matter in the binder has an influence on the porosity of the mix. When the binder contains a large amount of volatile matter, the mix becomes porous and is corroded seriously as the pig iron and slag pass through the tap hole. When the tap hole is opened before the volatile matter is completely removed from the furnace, or in other words, when the tap hole is opened by an opener before the carbon-carbon bonds of the binder have completely formed, the strength of unbaked portion of the tap hole mix is poor and the unbaked portion of the tar is exposed to sudden higher temperatures because of contact with molten pig iron and slag, so that black smoke and abnormal dusts are caused to occur, thus deteriorating the working environment. The abnormal dusts formation increases the corrosion and causes a rapid enlargement of the tap hole diameter, requiring operating the blast furnace at lowered furnace pressure and decreasing the amount blowing in, fluctuating the furnace conditions and reducing the productivity.
Since a tar bonded tap hole mix is also low in abrasion resistance against molten pig iron and slag as well as in its corrosion resistance, the dissolution loss of a tap hole plugged with the tar bonded mix is very large, and the tapping time per tapping must be shortened. In order to secure the desired goal of the total amount tapped per day, about 16 tappings are necessary per day, thus increasing the labour burden of the furnace operators.
A tap hole mix using a binder comprising tar (including pitch and asphalt) and a thermosetting resin has been developed in recent years. However, such a mix needs 30 minutes to exhibit a bending strength of more than 10 kg/cm.sup.2 at 600.degree. C, which is a goal of the mix having rapidly hardening property, and its hot bending strength is about 15 kg/cm.sup.2 at 1400.degree. C, so that said mix has various problems in applying particularly to a blast furnace in a high pressure operation. Its corrosion resistance is also about the same as a tar bonded mix. The tap hole suffers from an abnormal dissolution loss in applying said mix to a large size blast furnace with a tapping amount of more than 500 tons per one tapping, so that the tapping time must unavoidably be shortened, and consequently, the frequency of tapping per day increases and the labour burden increases. The furnace condition also deteriorates, and tuyere damage takes place.
It is considered that the troubles in mixes containing a binder which are obtained by adding a thermosetting resin to tar are due to the poor mutual solubility between the tar, pitch and asphalt and the thermosetting resin, and the condensation polymerisation reaction does not proceed smoothly under the coexistance of the two components.
As a result of detailed studies on the tap hole mix and considering the difficulties with the water containing mix, the tar bonded mix and the mix containing a binder obtained adding thermosetting resin to tar, the present inventors have succeeded in developing a tap hole mix having characteristics particularly suitable for a large size blast furnace and a blast furnace with a higher top pressure operation.